|[AMRadio] Hallicrafters HT-37 Alignment Question|
James M. Walker
chejmw at acsu.buffalo.edu
Sun Aug 22 22:30:57 EDT 2004
Hi Bill and List,
A couple of quick questions. First are all the mixer crystals in the
and the correct frequency? Note, if the crystals are in check to see
they are oscillating. If not first check the sockets they plug into,
for corrosion on the pins of the crystals. Also what is the RF voltage
level of the 9 Mhz at the 1st mixer is it correct? I suffered the
Screwdriver" syndrome here with mine, turned out the previous owner had
tightened the trimmer caps c65 c66, down all the way, guess he didn't
want the screw to come loose :~)
In conclusion, make sure the 9 Mhz is present at the 1st mixer, also
the VFO 5 Mhz output is where it should be coming out of T1, and then
the 2nd mixer. Hang in there as it will probably be something simple
you find it.
Bill Pancake wrote:
> Now that my Hallicrafters HT-37 has undergone it's cosmetic restoration successfully, it's time to tackle the alignment.
> It appears that someone before me has used the proverbial "golden screwdriver" to align it before. There is practically no output on any band except 15 meters (60 watts). The driver tube bias resistor R25 had been wired to ground instead of wired to the grid. Corrected that, but still no change in output.
> All tubes check OK by substituting known good tubes. Power supply has been restored with new electrolytics. All the black beauty caps were replaced as well. HV and LV tubes have been replaced with Weber "Copper Cap" rectifiers to take the load off the power xfmr. Gave the bandswitch a good cleaning and treated it with DeOxit. No change.
> Electrically, everything appears to be OK. HV, LV and bias supply voltages are good. PA bias in MOX/LSB position is -49vdc as recommended. In standby position, PA bias rises several volts as it should.
> I started to align it using an HP 606A rf signal generator and HP 410b VTVM following the procedures in the factory manual. The driver and 2nd mixer stages aligned as per manual. The 1st mixer 40m coil (L23) will not cause a PA grid voltage peak on the VTVM as it is adjusted like it is supposed to. Now I'm dead-in-the-water. Since I can't align the 1st mixer, I can go no further.
> >From those of you who have experience with HT-37 alignment, I'd almost sell my soul for a suggestion on what's wrong with the 1st mixer stage. L23 (40m coil) has good continuity and circuit wiring for that entire stage appears to be wired correctly.
> If there are other "lessons learned" in aligning an HT-37, or if I've missed a key procedure, please pass them on. There's no question in my mind that I'll take your advice if it's offered.
> I want to say many, many thanks to Al Parker, W8UT, who has already helped enormously with good advice, especially on the procedures for upgrading of the HT-37 power supply circuits. I've purchased another restorable HT-37 that hasn't been hacked-on from Al so I can do a side-by-side circuit wiring comparison.
> Since the previous owner of my HT-37 got creative with parts replacement wiring, I'm hoping that looking at both chassis' at the same time will help find the wiring mistakes. Can't hurt to have another HT-37 anyway.
> Thanks, Bill, ab0zz
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